Significant effort has been expended toward developing high power rechargeable batteries for use in hybrid electric vehicles and other such high power applications. Lithium ion batteries are capable of stably storing relatively large amounts of power, and efforts are being undertaken to fabricate practical, high power batteries employing lithium ion technology. However, the full potential of such battery technology has not been realized because of a shortage of appropriate electrode materials, particularly cathode materials.
A number of materials are currently being investigated for use as cathodes in high power lithium batteries, such as those employed in hybrid electric vehicles; and one such group of materials comprises lithiated transition metal phosphates such as LiFePO4. However, these materials have relatively low electrical conductivity, which restricts their use as electrode materials.
A number of attempts have been made in the prior art to increase the electrical conductivity of such materials by including metals or other elements either as dopants or as secondary components of the materials. In other instances, prior art materials have been employed in particular configurations in an attempt to accommodate their low electrical conductivity. Some prior art materials and configurations are shown in U.S. Pat. No. 6,514,640; 6,391,493; 6,447,951; 5,910,382 and 5,871,866; and in U.S. Patent Applications 2002/0195591 and 2003/0064287. Increases in electrical conductivity in such prior art materials are generally accompanied by a loss of volumetric charge storage capacity which limits the utility of these materials in high power batteries.
Accordingly, there is a need for improved materials which can be employed as a component of cathodes for lithium ion batteries. Such materials should have good electrical conductivity, be stable, easy to manufacture, low in cost and highly efficient. As will be described in detail hereinbelow, the present invention provides materials and methods which meet these requirements.